1. Field of the Invention
In one of its embodiments, this invention relates to processes of reducing the aldehyde content of amino resins by a process that does not cause any instability, such as gelation or formation of a precipitate, to occur in the amino resin after treatment or reduce the utility of the resins for their intended ultimate purpose. In another embodiment, the invention relates to compositions, which can be added to amino resins which have higher aldehyde contents than is desirable, in order to reduce their aldehyde content without (i) causing any instability, (ii) making the resin with reduced aldehyde less suitable for its intended use, or (iii) requiring any removal from the resin of the additive composition itself or any reaction products therefrom, in order to avoid impairing the intended useful properties thereof. Another embodiment of the inventions relates to amino resins that have had their aldehyde content reduced by a process according to the invention.
Still another embodiment of the invention relates to the detackification of paint and similar materials entrained in water, particularly circulating water in a conventional automobile plant spray booth, with the use of a process or product according to the invention as described above. "Paint" as used herein is to be understood as a generic term which encompasses all common varieties of water insoluble organic binder containing coatings commonly applied in spraying operations, including but not limited to oil based paints, enamels, lacquers, high solids solvent based automotive body base coat, high solids solvent based automotive body clear coat, water borne auto body base and clear coats, urethane polymer containing auto body top coats, and solvent and water borne primers. These paints may utilize asphaltic, acrylic, polyester, melamine-formaldehyde, isocyanate, epoxy, alkyd, melamine alkyd, and blocked polyurethane resins among others, along with appropriate solvents, pigments, and ancillary additives. Paint "overspray", the portion of the sprayed paint which does not fall on the surface(s) it is intended to protect, if left untreated, readily adheres to the walls of spray booths and to any other surfaces that it contacts, such as the surfaces of water distribution piping, spray nozzles, and the like. Use of a process according to this embodiment of the invention converts the paint overspray to a non-sticky sludge suitable for convenient disposal.
2. Statement of Related Art
For the purposes of this description, the term "amino resins", unless specifically limited, is to be understood to include (i) any collection of molecules that satisfies the following two conditions: (ii) at least some of the molecules have been formed or could be formed by at least one addition reaction between a molecule containing a --CHO (aldehydo) moiety and a molecule containing an amino (i.e., --NH.sub.2) moiety to form a single molecule product in which the nitrogen atom from the amino moiety has become covalently bonded to the carbon atom from the aldehydo moiety and (iii) the entire collection of molecules is capable of further reaction, without the addition of any outside ingredients, to form polymer molecules, each of which contains at least 10 nitrogen atoms and (ii) all liquid solutions and dispersions, in water or other compounds that are liquid at normal atmospheric pressure at a temperature of 20.degree. C., of materials that are amino resins according to the definition of part (i) of this sentence. When necessary to distinguish between these two classes of amino resins, the latter class will be denoted herein as "amino resin dispersions" and the former class as "amino resins, solids basis".
In commercially available amino resins, the aldehyde is almost always formaldehyde, and most of the remainder of this specification will therefore be directed toward resins in which all or most of the aldehyde molecules from which the resin was or could be formed are formaldehyde molecules. However, this description is meant to apply, mutatis mutandis, to resins with other types of aldehydes.
A much more diverse group of amino group containing compounds, many of which are themselves amino resins according to the definition given above, are used to form commercially available or otherwise previously known types of amino resins. These include, but are not necessarily limited to, urea, alkyl substituted ureas, thiourea and alkyl substituted thiourea, melamine, benzoguanamine, ethyleneurea (i.e., 2-imidazolidinone), dimethylolethyleneurea (i.e., 1,3-bis[hydroxymethyl]-2-imidazolidinone), propyleneurea (i.e., tetrahydro-2-pyrmidinone), dimethylolpropyleneurea (i.e., 1,3-bis[hydroxymethyl]tetrahydro-2-pyrmidinone), methylol urea, dimethylol urea, acetoguanamine, acrylamide, N-methylolacrylamide, aniline, toluene sulfonamide, N,N'-dimethylol derivatives of tetrahydro-5-alkyl-s-triazones, 1,3-bis(methoxymethyl)uron, and 1,3-bis(hydroxymethyl)-4,5-dihydroxy-2-imidazolidinone (also known as "dimethyloldihydroxyethyleneurea" or "DMDHEU"), and trimethylolmelamine and ethers thereof. Most of the remainder of the description will focus on melamineformaldehyde resin, because they are particularly preferred in the specialized field of paint detackifying, to which one embodiment of this invention is directed. However, the description should be understood as applying, mutatis mutandis, to other amine-aldehyde, and particularly other amine-formaldehyde, oligomers and polymers.
It is known in the art to use a melamine-aldehyde polymer, particularly a melamine-formaldehyde resin acid colloidal solution, as an effective treatment for detackification. However, the previously known polymers of this type made from formaldehyde usually contain substantial amounts of free formaldehyde. For example, most commercial liquid melamine-formaldehyde resins contain at least 0.2% by weight of free formaldehyde. (Hereinafter, all percentages are to be understood as percentages by weight unless otherwise stated.) Formaldehyde is believed to be a carcinogen, so that use of materials containing more than a minimal amount of it is undesirable in general.